Mass motions (also dubbed mass-wasting) is the down-slope motion of Regolith (loose uncemented mixture the soil and rock particles that covers the Earth"s surface) by the force of heaviness without the assist of a transporting medium such together water, ice, or wind. Still, as we chandelier see, water dram a vital role.

Mass movements are part of a continually of erosional processes between weathering and stream transport. Massive movement causes regolith and rock to relocate down-slope wherein sooner or later on the loose particles will be picked up by an additional transporting agent and also eventually relocated to a website of deposition such together an ocean basin or lake bed.

You are watching: The downslope movement of rock or soil due to the influence of gravity is

Mass activity processes are developing continuously on every slopes; some act an extremely slowly, others occur very suddenly, regularly with devastating results.

In this discussion, we hope to answer the following questions:

What determines whether or no a steep is secure or unstable? how are the various mass movement processes classified? how are fixed movement occasions triggered? What observations might suggest the the area is unstable and also may start to move? How deserve to we mitigate against mass motion hazards?

We start with a conversation of the pressures acting at the surface ar that reason mass movements.


Gravity is the main force responsible for mass movements.

Gravity is a pressure that acts anywhere on the Earth"s surface, pulling everything in a direction towards the center of the Earth. ~ above a flat surface, parallel to the Earth"s surface, the pressure of heaviness acts downward. So long as the material remains ~ above the flat surface it will certainly not move under the force of gravity. Of course if the material forming the flat surface becomes weak or fails, climate the unsupported support mass will relocate downward.
On a slope, the force of gravity have the right to be resolved right into two components: a component acting perpendicular come the slope, and also a component acting parallel come the slope.


The perpendicular component of gravity, gp, help to hold the thing in ar on the slope. The component of gravity exhilaration parallel come the slope, gs, causes a shear tension parallel to the slope and helps to move the object in the down-slope direction. on a steeper slope, the shear anxiety component that gravity, gs, increases, and the perpendicular component of gravity, gp, decreases. an additional force resisting activity down the steep is grouped under the hatchet shear strength and also includes friction resistance and also cohesion amongst the particles that make up the object. once the sheer stress and anxiety becomes greater than the combination of forces holding the object on the slope, the thing will relocate down-slope. Thus, down-slope activity is favored by steeper slope angle (increasing the shear stress) and anything that reduces the shear strength (such as lowering the cohesion among the particles or lowering the frictional resistance. because that unconsolidated material, the angle that develops a secure slope is referred to as the angle that repose.

The duty of Water

Although water is not constantly directly involved as the transporting tool in mass activity processes, it does play an essential role. Addition of water from rainfall or eye melt adds load to the slope. Water have the right to seep into the soil or rock and also replace the waiting in the pore space or fractures.Since water is heavier than air, this boosts the load of the soil.If the material becomes saturated with water, vibrations could reason liquifaction come occur, similar to often happens throughout earthquakes. Water deserve to reduce the friction along a sliding surface.Water has the ability to readjust the angle of repose (the slope edge which is the secure angle for the slope).

Think around building a sand castle on the beach. If the sand is entirely dry, it is difficult to develop a heap of sand with a steep challenge like a castle wall. If the sand is rather wet, however, one can build a vertical wall. If the sand is too wet, climate it flows choose a fluid and cannot stay in place as a wall.

dried unconsolidated seed will kind a pile v a steep angle identified by the angle the repose. The angle of repose is the steepest edge at which a heap of unconsolidated grains continues to be stable, and is regulated by the friction contact between the grains. In general, because that dry products the edge of repose boosts with increasing grain size, however usually lies between about 30 and also 45 o. Coarser grained and also angular particles have actually a steeper edge of repose than fine grained and also rounded particles.


Another product that shows similar swelling and also compaction as a an outcome of addition or remove of water is peat. Peat is organic-rich material accumulated in the bottoms of swamps together decaying vegetables matter.

sensitive Soils - In some soils the clay minerals room arranged in arbitrarily fashion, with much pore room between the individual grains.This is regularly referred to as a "house that cards" structure. Regularly the seed are organized in this position by salt (such together gypsum, calcite, or halite) precipitation in the pore space that "glue" the particles together.As water infiltrates into the pore spaces, as disputed above, it have the right to both be took in onto the clay minerals, and can dissolve far the salt holding the "house of cards" together.


Compaction that the soil or shiver of the soil deserve to thus cause a rapid readjust in the framework of the material. The clay minerals will then line up through one another and also the open an are will it is in reduced.

But this may reason a ns in shear stamin of the floor and an outcome in slippage under slope or liquefaction.

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part water saturation clays room stable so long as castle aren’t disturbed, but when shaking occurs, as with sands, they can turn into a runny fluid. This are described as quick clays.

Weak Materials and also Structures

Rocks often contain planar frameworks that become slippage surfaces if weight is added or assistance is removed.